In general, electronic endoscopes are configured by including a solid-state image pickup device, such as CCD, for imaging an observation object at a distal end of an insertion portion of the electronic endoscope, and are configured to output an image signal output from the solid-state image pickup device to a monitor or the like as an external device, and thereby making the image signal displayed as an observation image.
For example, in the endoscope disclosed in Japanese Patent Laid-Open No. 2000-14635, a circuit board for driving a solid-state image pickup device is connected to a distal end of a signal cable (signal line) for transmitting an image signal picked up by the solid-state image pickup device, behind the solid-state image pickup device at the distal end portion of the insertion portion of the endoscope. The solid-state image pickup device, the circuit board, and the distal end of the signal cable are arranged inside a shield frame which is a frame body for fixing these portions. Further, an objective optical system unit having an objective lens for forming an optical image of an object on the light receiving surface of the solid-state image pickup device is provided in front of the shield frame. In the following, a portion configured by combining the solid-state image pickup device, the circuit board, the signal cable, the shield frame, and the objective optical system unit is referred to as an image pickup apparatus for the sake of convenience.
The image pickup apparatus is fitted from behind into a stepped through hole provided in the distal end portion main body forming the distal end portion of the insertion portion, so as to be attached. Further, a V-shaped fixing groove is formed in the outer peripheral surface of the objective optical system unit. On the other hand, a fixing screw is arranged in a portion of the distal end main body, which portion faces the fixing groove. The fixing screw is screwed in the radial direction of the objective optical system unit, so as to abut against the fixing groove, whereby the distal end portion main body and the image pickup apparatus including the objective optical system unit are fixed to each other.
According to the technique disclosed in Japanese Patent Laid-Open No. 2000-14635, the stepped through hole provided in the distal end portion main body has a shape corresponding to the external shape of the image pickup apparatus. For this reason, the combination of the image pickup apparatus and the distal end portion main body is limited only to the case where they are in one to one correspondence. In the electronic endoscope having such a configuration, it is impossible to replace the image pickup apparatus with, for example, another image pickup apparatus having a shape different from that of the original one and including a different number of pixels therefrom and a lens system of a viewing angle different therefrom. That is, when an endoscope user intends to use the electronic endoscope in combination with an image pickup apparatus of different specification, for example, with an image pickup apparatus having an external shape which is made smaller than the external shape of the originally provided image pickup apparatus because of a change in at least one of the solid-state image pickup device and the objective optical system unit, the endoscope user needs to separately purchase an electronic endoscope of different specification.
The present invention has been made in order to solve the above described problem. An object of the present invention is to provide an electronic endoscope capable of easily replacing the image pickup apparatus of the electronic endoscope with an image pickup apparatus of different specification.